Powderpost Beetle

Introduction:

Lyctids are commonly known as (true) powderpost beetles because their larvae produce a very fine, powderlike frass in their galleries (vs. bostrichids/false powderpost beetles and anobiids, whose larvae produce coarser frass which also contains fine wood fragments or pellets respectively). They are worldwide in distribution, with about 11 species occurring in the United States.

Recognition

Depending on the species, adults about 1/32-1/4" (1-7 mm) long. Body elongate, narrow, flattened, almost parallel-sided; head, pronotum, and elytra (wing covers) about equal in width; pronotum somewhat wider at front, head and often mandibles visible when viewed from above. Color reddish brown to black. Antennae with abrupt 2-segmented club. Elytra (wing covers) often with rows of hairs (setae). First abdominal segment ventrally much longer than other segments.

Depending on the species, mature larvae up to about 1/4" (6 mm) long. Color nearly white. Body C-shaped but with enlarged thorax. Antennae short, 4-segmented. Spiracle of 8th (last) abdominal segment 3 times larger than other abdominal spiracles. Legs 3-segmented, ending with a long claw. However, 1st instar larva straight-bodied, white, and bears a pair of small spines at rear end.

Similar Groups

(1) Flat bark beetles (Cucujidae) with antennae usually long and threadlike/beadlike, sometimes short with 2-4-segmented club, elytra (wing covers) usually lack hairs.

(2) False powderpost beetles (Bostrichidae) usually cylindrical in form, pronotum with rasplike teeth at front, head usually not visible from above.

Damage And SIgns Of Infestation

Exit holes are round, and depending on the species, range from 1/32-1/16" (0.8-1.6 mm) in diameter. Another indication of an infestation is the accumulation of piles of very fine powderlike dust beneath the exit holes or on the wood. This dust/frass contains no pellets (like anobiid's) and falls easily from the hole instead of being packed in (like anobiids and bostrichids).

Biology

Female Iyctids lay their eggs (15-50) in exposed wood pores, cracks, or crevices. Eggs are never deposited in/on waxed, polished, painted, or varnished surfaces. The larvae tunnel only in the sapwood and usually tunnel with the wood grain. As they bore, the larvae loosely pack their tunnels with very fine powderlike dust (like talcum powder or flour). After several molts requiring 2-9 months, the mature larva bores to near the surface and constructs a pupal chamber and pupates. When the adult emerges, it bores straight to the wood's surface and exits/emerges. Indoors, adults usually emerge in late winter or early spring and with little feeding, mate. Under very favorable conditions, developmental time (egg to adult) usually requires 9-12 months, but may be as short as 3-4 months or as long as 2.5-4 or more years. Although some Iyctids are strong fliers, most tend to lay eggs in the wood from which they emerged. Since Iyctid larvae cannot digest cellulose, they feed only on the cell contents which is primarily starch, but also sugar and protein.

Habits

Lyctids attack the sapwood and only that of hardwoods, usually less than 10 years old. They attack both lumber and manufactured products; they also attack structural timbers but hardwoods are rarely used for this purpose today because of their cost. The wood moisture content required for beetle development is 8-32%, with greatest activity at 10-20%. Adults are active at night, readily fly, and are attracted to light.

Control

Pesticide Treatment: In order to effectively manage powder post beetles and other wood-destroying beetles, pesticides with high penetration capability and extended residual longevity such as Bora-Care® and Tim-bor® (a slow acting stomach poison) need to be used. Even so, Bora-Care® or other liquid pesticides do not penetrate wood has polyurethane finish, paint, varnish or a water-repellent stain. They need to be applied only to bare wood, plywood, particleboard, and other cellulosic surfaces. Therefore, infested finished wood must be stripped before treatment and re-coated afterward.

If the finishes cannot be removed, deep penetration is still needed to manage the developing larvae inside the wood. In this situation, the wood surface can be drilled and the Bora-Care® or Jecta Gel® (a concentrated form of Bora-Care® in a gel base that is delivered by a plastic syringe) is applied inside the holes. These holes need to be sealed after treatment or the gel will leak out.

In case of severe, extended, and rapid elimination of powder post beetles is desired, especially when other methods have failed, a fumigation is another option to be considered for managing these insects; however, fumigation does not prevent from re-infestation of the wood, thus, treat with Bora-Care® to prevent future infestation. Note that fumigation requires special preparations and precaution measures before treatment.

For thin pieces (baskets and wreathes), adult exit holes can be treated individually with a crack and crevice aerosol (e.g., Invader). It is also recommended to treat with Bora-Care® later to ensure longer residual effects. However, homeowners, building managers or their agents, need to know that the treatment with Bora-Care® will stop the development of the chewing larvae quickly and prevent later infestation, but adults may be still seen for a while until all developing pupae have emerged.